Synthesis of 2-alkynyl substituted 4′-thioadenosine derivatives and their binding affinities at the adenosine receptors

On the basis of high binding affinity of 2-hexynyl-N(6)-methyladenosine and N(6)-substituted-4'-thioadenosine derivatives at the A3 adenosine receptor (AR), novel 2-alkynyl-substituted-N(6)-methyl-4'-thioadenosine derivatives, combining the characteristics of two classes of nucleosides were designed and synthesized from D-gulonic gamma-lactone via palladium-catalyzed cross coupling reaction as a key step. Among compounds tested, only compound 3b showed moderate binding affinity at the human A3 adenosine receptor without binding affinities at other subtypes.